How to Fix The following signatures couldn’t be verified Error in Ubuntu Linux | The following signatures couldn’t be verified Error in Ubuntu Linux

W: GPG error: https://pkg.jenkins.io/debian-stable binary/ Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY FCEF32E745F2C3D5
E: The repository 'http://pkg.jenkins.io/debian-stable binary/ Release' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.

Fix GPG error: The following signatures couldn’t be verified

What we need to do is to fetch this public key in the system. Get the key number from the message. In the above message, the key is XXXXXXXXXXX. Now use that key in the following command:

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys XXXXXXXXXXX

This will add the key to the system. and then perform update

 sudo apt-get update 

and you should not see this error any more. I hope this solved the problem .